Digital watermarking is the science of encoding physical and electronic objects with plural-bit digital data, in such a manner that the data is essentially hidden from human perception, yet can be recovered by computer analysis. In physical objects, the data may be encoded in the form of surface texturing, or printing. Such marking can be detected from optical scan data, e.g., from a scanner or web cam. In electronic objects (e.g., digital audio or imagery—including video), the data may be encoded as slight variations in sample values. Or, if the object is represented in a so-called orthogonal domain (also termed “non-perceptual,” e.g., MPEG, DCT, wavelet, etc.), the data may be encoded as slight variations in quantization values or levels. The present assignee's patents U.S. Pat. Nos. 6,122,403 and 6,408,082, and application Ser. No. 09/503,881 (now U.S. Pat. No. 6,614,914), are illustrative of certain watermarking technologies. Watermarking techniques are also taught in the following Philips patents: U.S. Pat. Nos. 6,252,972, 6,209,092, 6,198,832, 6,157,330, 6,131,161, 6,031,815, 5,940,134, 5,933,798, and 5,873,022.
Watermarking can be used to tag objects with a persistent digital identifier, and as such finds myriad uses. Some are in the realm of device control—e.g., tagging video data with a do-not-copy flag that is respected by compliant video recorders. (The music industry's Secure Digital Music Initiative (SDMI), and the motion picture industry's Copy Protection Technical Working Group (CPTWG), are working to establish standards relating to watermark usage for device control.) Other watermark applications are in the field of copyright communication, e.g., indicating that an audio track is the property of a particular copyright holder.
Other watermark applications encode data that serves to associate an object with a store of related data. For example, an image watermark may contain an index value that serves to identify a database record specifying (a) the owner's name; (b) contact information; (c) license terms and conditions, (d) copyright date, (e) whether adult content is depicted, etc., etc. (The present assignee's MarcCentre service provides such functionality.) Related are so-called “connected content” applications, in which a watermark in one content object (e.g., a printed magazine article) serves to link to a related content object (e.g., a web page devoted to the same topic). The watermark can literally encode an electronic address of the related content object, but more typically encodes an index value that identifies a database record containing that address information. application Ser. No. 09/571,422 (now U.S. Pat. No. 6,947,571) details a number of connected-content applications and techniques.